9 ms·

Humans evolved to tolerate smoke poisoning [pdf]

70 points by gwern 10y ago

pcrh 10y ago
This is interesting. I wonder if the tolerance of the mouth to heat (relative to other areas with a thin epidermis) is also related to cooking.
VeejayRampay 10y ago
The way the title is phrased is strange. To the young/uneducated reader (not so many around here, but still), it reads like humans evolve to develop a particular trait, when we know that people who developed that trait got an evolutionary advantage and ended up spreading their DNA more than others on average. Not as catchy a title, sure, but at least, it doesn't misrepresent the evolutionary process. NOTE: I am not an evolutionary biologist, so there is most likely an even better way to rephrase my rephrasing. I'd be glad for anyone to do so, the more accurate, the better.
- posterboy 10y ago
  > it reads like humans evolve to develop a particular trait, when we know that people who developed that trait got an people who developed that trait had to evolve to do so, no? Not as an entire population, but maybe over the live span of individuals. Maybe the smoke itself caused that, as exposure often does, "evolving" in some individuals who then pass immunity markers down over generations through blood in the womb rather than genetically. Or maybe the smoke is cancerous and caused beneficial mutations. I should read the paper (edit: it says genetic). All I'm trying to say is, either development is subsumed under evolution.
  - inimino 10y ago
    > people who developed that trait had to evolve to do so, no? The word "evolve" in English means a gradual change, so no. Random genetic mutation isn't a response to the smoke, and there isn't anybody born unadapted who then adapts by exposure. The species evolves, individuals don't.
    - nonbel 10y ago
      >"The species evolves, individuals don't." You are made of cells that are many generations separated from the fertilized egg. I don't see why you accept evolution at the species level but not cell level. This sounds like a kind of reverse creationism, where macro-evolution is ok but micro-evolution is not.
      - inimino 10y ago
        Um, honestly not sure what you're getting at there. The individual cells in your body are genetically the same as what you started with, with occasional random mutations. The body defends itself against those mutations and most will be eliminated. Some will become cancers. They don't affect the DNA you pass on to your offspring and so aren't a part of the evolution of your species. None of them are going to give you superpowers unless you happen to be living in a comic book.
        nonbel 10y ago
        Say a person is exposed to smoke often since being a young child. At some point, a lung cell is dividing and randomly gains a mutation that increases expression of some smoke-protective protein. This lung cell is then more fit (to the smokey environment) than the surrounding lung cells. As a result, its daughter cells will divide more often than the others and populate the tissue. Are you denying this can happen? Or is it that you do not consider that process to be evolution?
        alecmckinley 10y ago
        That absolutely can happen - but remember that the traits of the 'evolved' lung cell will not be passed to offspring, as the genetic makeup of gametes (sperm) is a random (50%) subset of the main genetic code.
        nonbel 10y ago
        Sure, but the population of cells we call an individual human being does "evolve" over the course of its life.
  - logfromblammo 10y ago
    Evolution occurs via reproduction over the span of many generations. Individual adaptation on a single-lifespan scale occurs via epigenetic methylation tagging of the existing (evolved) genome. You cannot become better adapted to smoke unless your genome already contains a gene that mitigates the damage, or a gene that can regulate expression of a damage-mitigating gene based on that specific stimulus. So if you breathe smoke frequently over your lifespan, you may have a gene related to mucus in the lungs expressing its protein at maximum capacity 24-7, while someone who never breathes smoke has that gene "turned off" most of the time. Transfer of individual adaptations, usually in the form of antibodies that can teach immune cells to respond to a specific hazard, is very limited, and will only last as long as that specific threat is continuously endemic. We have mostly supplanted that natural capacity with artificial vaccinations. Random mutations are usually harmful. Sexual reproduction and selection is the mechanism to shuffle the most harmful mutations out of the genome while still retaining the rare beneficial mutation. If the mutation rate is too low, the species cannot evolve quickly enough in changing environments. If the mutation rate is too high, sexual reproduction cannot eliminate the bad mutations fast enough.
- patrickg_zill 10y ago
  I think you are saying that there is no teleology in the theory of evolution.
- inimino 10y ago
  > humans evolve to develop a particular trait > people who developed that trait got an evolutionary advantage and ended up spreading their DNA more than others on average. The first is shorthand for the second.
  - VeejayRampay 10y ago
    Ah OK, my bad then.
  - iand 10y ago
    It's sloppy shorthand though because it can be (deliberately) misconstrued to suggest agency and directional purpose.
fsloth 10y ago
" Our findings reveal that a functionally significant change in the AHR occurred uniquely in humans, relative to other primates, that would attenuate the response to many environmental pollutants, including chemicals present in smoke from fire use during cooking. " So we have some genetic tolerance to bad stuff created from cooking? Cool. This does, however, raise ever more questions about studying the effects of chemicals on rats and primates and drawing conclusions from that to human populations.
- Bartweiss 10y ago
  This seems like a really good question to raise, and I'm embarrassed that I didn't think of it at all. I know carcinogen studies are already touchy since cancer risks vary so wildly, but this is a nice reminder that even within primates you get this kind of problem.
a_bonobo 10y ago
I don't buy the smoke poisoning angle. They compared with Neandertal AHRs and found that human AHRs may have undergone selective pressures since they're quite different, so the authors tried to connect these changes with the invention of fire. However AHRs bind to many things. Also, Neandertals also used fire extensively (see for example http://www.pnas.org/content/108/13/5209 http://www.pnas.org/content/108/13/5209 ) so they should have undergone the same selective pressures, so they should have the same or similar changes as humans?
- AimHere 10y ago
  Might the selection pressure have been fire related, without necessarily being just the use of fire? If, for one speculative example, Neanderthals mostly used fire outdoors, while modern humans used it indoors with correspondingly thicker smoke concentrations, wouldn't that account for the difference? Or perhaps only a few Neanderthals out of any given population used it regularly (for crafting tools, say), while almost all modern humans could have used it for cooking food.
  - a_bonobo 10y ago
    I see! But that's a bit hard to prove, isn't it? I don't think we have enough archaeological sites with proven fire places to prove that assumption
Houshalter 10y ago
Smoke still is bad for humans though, see this essay: https://www.samharris.org/blog/item/the-fireplace-delusion/ https://www.samharris.org/blog/item/the-fireplace-delusion/ >There is no amount of wood smoke that is good to breathe. It is at least as bad for you as cigarette smoke, and probably much worse. (One study found it to be 30 times more potent a carcinogen.) The smoke from an ordinary wood fire contains hundreds of compounds known to be carcinogenic, mutagenic, teratogenic, and irritating to the respiratory system. Most of the particles generated by burning wood are smaller than one micron—a size believed to be most damaging to our lungs. In fact, these particles are so fine that they can evade our mucociliary defenses and travel directly into the bloodstream, posing a risk to the heart. Particles this size also resist gravitational settling, remaining airborne for weeks at a time. >Once they have exited your chimney, the toxic gases (e.g. benzene) and particles that make up smoke freely pass back into your home and into the homes of others. (Research shows that nearly 70 percent of chimney smoke reenters nearby buildings.) Children who live in homes with active fireplaces or woodstoves, or in areas where wood burning is common, suffer a higher incidence of asthma, cough, bronchitis, nocturnal awakening, and compromised lung function. Among adults, wood burning is associated with more-frequent emergency room visits and hospital admissions for respiratory illness, along with increased mortality from heart attacks. The inhalation of wood smoke, even at relatively low levels, alters pulmonary immune function, leading to a greater susceptibility to colds, flus, and other respiratory infections. All these effects are borne disproportionately by children and the elderly. >In the developing world, the burning of solid fuel in the home is a genuine scourge, second only to poor sanitation as an environmental health risk. In 2000, the World Health Organization estimated that it caused nearly 2 million premature deaths each year—considerably more than were caused by traffic accidents.
- raverbashing 10y ago
  Of course it's not good But if your options are, stay close to the fire or die, that's an important selective pressure
- hvidgaard 10y ago
  I'm sure there is some truth to the article, but it paints a very different picture than the referenced paper at the buttom. > Finally, returning to the questions posed at the start, we conclude that although there is a large and growing body of evidence linking exposure to wood/biomass smoke itself with both acute and chronic illness, there is insufficient evidence at present to support regulating it separately from its individual components, especially fine particulate matter. In addition, there is insufficient evidence at present to conclude that woodsmoke particles are significantly less or more damaging to health than general ambient fine particles. > Nevertheless, given the importance of woodsmoke as a contributor to particle concentrations in many locations, strategies to reduce woodsmoke emissions may be an effective means of lowering particle exposures. In addition, given the weight of toxicologic evidence, additional epidemiologic studies are needed to confirm our conclusions.
Dowwie 10y ago
Lung cancer?
deleted 10y ago
[deleted]
belorn 10y ago
Reminds me of a story where Robert Sapolsky, a professor in biology when he was staying in a native African hut and decided to put out the indoor fire before sleeping, since he was concerned about the smoke. Later during the night he woke up, covered in driver ants, realizing very fast the reason why the natives sleep with the huts full of smoke.
detritus 10y ago
I've often wondered whether something similar might be at play in relation to the supposed cancer risks from acrylamides forming in burnt food. Sure, the stuff's poisonous to rats etc, but given our physiology has evolved smaller intestinal tracts and larger brains in relation to cooked foods (particularly, meat), might it also be that we're less susceptible to its cancerous potential than other mammals?

70 points by gwern 10y ago

pcrh 10y ago

This is interesting. I wonder if the tolerance of the mouth to heat (relative to other areas with a thin epidermis) is also related to cooking.

VeejayRampay 10y ago

The way the title is phrased is strange. To the young/uneducated reader (not so many around here, but still), it reads like humans evolve to develop a particular trait, when we know that people who developed that trait got an evolutionary advantage and ended up spreading their DNA more than others on average. Not as catchy a title, sure, but at least, it doesn't misrepresent the evolutionary process. NOTE: I am not an evolutionary biologist, so there is most likely an even better way to rephrase my rephrasing. I'd be glad for anyone to do so, the more accurate, the better.

posterboy 10y ago
> it reads like humans evolve to develop a particular trait, when we know that people who developed that trait got an people who developed that trait had to evolve to do so, no? Not as an entire population, but maybe over the live span of individuals. Maybe the smoke itself caused that, as exposure often does, "evolving" in some individuals who then pass immunity markers down over generations through blood in the womb rather than genetically. Or maybe the smoke is cancerous and caused beneficial mutations. I should read the paper (edit: it says genetic). All I'm trying to say is, either development is subsumed under evolution.
- inimino 10y ago
  > people who developed that trait had to evolve to do so, no? The word "evolve" in English means a gradual change, so no. Random genetic mutation isn't a response to the smoke, and there isn't anybody born unadapted who then adapts by exposure. The species evolves, individuals don't.
  - nonbel 10y ago
    >"The species evolves, individuals don't." You are made of cells that are many generations separated from the fertilized egg. I don't see why you accept evolution at the species level but not cell level. This sounds like a kind of reverse creationism, where macro-evolution is ok but micro-evolution is not.
    - inimino 10y ago
      Um, honestly not sure what you're getting at there. The individual cells in your body are genetically the same as what you started with, with occasional random mutations. The body defends itself against those mutations and most will be eliminated. Some will become cancers. They don't affect the DNA you pass on to your offspring and so aren't a part of the evolution of your species. None of them are going to give you superpowers unless you happen to be living in a comic book.
      - nonbel 10y ago
        Say a person is exposed to smoke often since being a young child. At some point, a lung cell is dividing and randomly gains a mutation that increases expression of some smoke-protective protein. This lung cell is then more fit (to the smokey environment) than the surrounding lung cells. As a result, its daughter cells will divide more often than the others and populate the tissue. Are you denying this can happen? Or is it that you do not consider that process to be evolution?
        alecmckinley 10y ago
        That absolutely can happen - but remember that the traits of the 'evolved' lung cell will not be passed to offspring, as the genetic makeup of gametes (sperm) is a random (50%) subset of the main genetic code.
        nonbel 10y ago
        Sure, but the population of cells we call an individual human being does "evolve" over the course of its life.
- logfromblammo 10y ago
  Evolution occurs via reproduction over the span of many generations. Individual adaptation on a single-lifespan scale occurs via epigenetic methylation tagging of the existing (evolved) genome. You cannot become better adapted to smoke unless your genome already contains a gene that mitigates the damage, or a gene that can regulate expression of a damage-mitigating gene based on that specific stimulus. So if you breathe smoke frequently over your lifespan, you may have a gene related to mucus in the lungs expressing its protein at maximum capacity 24-7, while someone who never breathes smoke has that gene "turned off" most of the time. Transfer of individual adaptations, usually in the form of antibodies that can teach immune cells to respond to a specific hazard, is very limited, and will only last as long as that specific threat is continuously endemic. We have mostly supplanted that natural capacity with artificial vaccinations. Random mutations are usually harmful. Sexual reproduction and selection is the mechanism to shuffle the most harmful mutations out of the genome while still retaining the rare beneficial mutation. If the mutation rate is too low, the species cannot evolve quickly enough in changing environments. If the mutation rate is too high, sexual reproduction cannot eliminate the bad mutations fast enough.
patrickg_zill 10y ago
I think you are saying that there is no teleology in the theory of evolution.
inimino 10y ago
> humans evolve to develop a particular trait > people who developed that trait got an evolutionary advantage and ended up spreading their DNA more than others on average. The first is shorthand for the second.
- VeejayRampay 10y ago
  Ah OK, my bad then.
- iand 10y ago
  It's sloppy shorthand though because it can be (deliberately) misconstrued to suggest agency and directional purpose.

fsloth 10y ago

" Our findings reveal that a functionally significant change in the AHR occurred uniquely in humans, relative to other primates, that would attenuate the response to many environmental pollutants, including chemicals present in smoke from fire use during cooking. " So we have some genetic tolerance to bad stuff created from cooking? Cool. This does, however, raise ever more questions about studying the effects of chemicals on rats and primates and drawing conclusions from that to human populations.

Bartweiss 10y ago
This seems like a really good question to raise, and I'm embarrassed that I didn't think of it at all. I know carcinogen studies are already touchy since cancer risks vary so wildly, but this is a nice reminder that even within primates you get this kind of problem.

a_bonobo 10y ago

I don't buy the smoke poisoning angle. They compared with Neandertal AHRs and found that human AHRs may have undergone selective pressures since they're quite different, so the authors tried to connect these changes with the invention of fire. However AHRs bind to many things. Also, Neandertals also used fire extensively (see for example http://www.pnas.org/content/108/13/5209 http://www.pnas.org/content/108/13/5209 ) so they should have undergone the same selective pressures, so they should have the same or similar changes as humans?

AimHere 10y ago
Might the selection pressure have been fire related, without necessarily being just the use of fire? If, for one speculative example, Neanderthals mostly used fire outdoors, while modern humans used it indoors with correspondingly thicker smoke concentrations, wouldn't that account for the difference? Or perhaps only a few Neanderthals out of any given population used it regularly (for crafting tools, say), while almost all modern humans could have used it for cooking food.
- a_bonobo 10y ago
  I see! But that's a bit hard to prove, isn't it? I don't think we have enough archaeological sites with proven fire places to prove that assumption

Houshalter 10y ago

Smoke still is bad for humans though, see this essay: https://www.samharris.org/blog/item/the-fireplace-delusion/ https://www.samharris.org/blog/item/the-fireplace-delusion/ >There is no amount of wood smoke that is good to breathe. It is at least as bad for you as cigarette smoke, and probably much worse. (One study found it to be 30 times more potent a carcinogen.) The smoke from an ordinary wood fire contains hundreds of compounds known to be carcinogenic, mutagenic, teratogenic, and irritating to the respiratory system. Most of the particles generated by burning wood are smaller than one micron—a size believed to be most damaging to our lungs. In fact, these particles are so fine that they can evade our mucociliary defenses and travel directly into the bloodstream, posing a risk to the heart. Particles this size also resist gravitational settling, remaining airborne for weeks at a time. >Once they have exited your chimney, the toxic gases (e.g. benzene) and particles that make up smoke freely pass back into your home and into the homes of others. (Research shows that nearly 70 percent of chimney smoke reenters nearby buildings.) Children who live in homes with active fireplaces or woodstoves, or in areas where wood burning is common, suffer a higher incidence of asthma, cough, bronchitis, nocturnal awakening, and compromised lung function. Among adults, wood burning is associated with more-frequent emergency room visits and hospital admissions for respiratory illness, along with increased mortality from heart attacks. The inhalation of wood smoke, even at relatively low levels, alters pulmonary immune function, leading to a greater susceptibility to colds, flus, and other respiratory infections. All these effects are borne disproportionately by children and the elderly. >In the developing world, the burning of solid fuel in the home is a genuine scourge, second only to poor sanitation as an environmental health risk. In 2000, the World Health Organization estimated that it caused nearly 2 million premature deaths each year—considerably more than were caused by traffic accidents.

raverbashing 10y ago
Of course it's not good But if your options are, stay close to the fire or die, that's an important selective pressure
hvidgaard 10y ago
I'm sure there is some truth to the article, but it paints a very different picture than the referenced paper at the buttom. > Finally, returning to the questions posed at the start, we conclude that although there is a large and growing body of evidence linking exposure to wood/biomass smoke itself with both acute and chronic illness, there is insufficient evidence at present to support regulating it separately from its individual components, especially fine particulate matter. In addition, there is insufficient evidence at present to conclude that woodsmoke particles are significantly less or more damaging to health than general ambient fine particles. > Nevertheless, given the importance of woodsmoke as a contributor to particle concentrations in many locations, strategies to reduce woodsmoke emissions may be an effective means of lowering particle exposures. In addition, given the weight of toxicologic evidence, additional epidemiologic studies are needed to confirm our conclusions.

Dowwie 10y ago

Lung cancer?

deleted 10y ago

[deleted]

belorn 10y ago

Reminds me of a story where Robert Sapolsky, a professor in biology when he was staying in a native African hut and decided to put out the indoor fire before sleeping, since he was concerned about the smoke. Later during the night he woke up, covered in driver ants, realizing very fast the reason why the natives sleep with the huts full of smoke.

detritus 10y ago

I've often wondered whether something similar might be at play in relation to the supposed cancer risks from acrylamides forming in burnt food. Sure, the stuff's poisonous to rats etc, but given our physiology has evolved smaller intestinal tracts and larger brains in relation to cooked foods (particularly, meat), might it also be that we're less susceptible to its cancerous potential than other mammals?